1. Field of the Invention.
The present invention relates to self-aligning grips for specimen testing machines.
2. Description of the Prior Art.
In the prior art, hydraulic cylinders that act in parallel to permit swiveling for alignment for testing machine grips are known. U.S. Pat. No. 1,865,070 shows pistons and cylinders that act in parallel with respect to a pullrod system for a tensile test, so that the force on the pullrods is equalized, and misalignment of the grip is minimized. The individual hydraulic cylinder and piston assemblies increase manufacturing costs, require a larger number of sealing surfaces, thus having a larger number of seals that are required, and in addition they provide more opportunity for binding.
Additionally, self aligning grips that use spherical seats are shown in U.S. Pat. No. 3,320,798 which uses a spherical seat cylinder for permitting alignment of the grip relative to the actuator rod, and then fluid pressure is used to lock the spherical seat parts in place with hydraulic pressure.
U. S. Pat. No. 1,023,154 to Kenerson shows a hydrostatic weighing machine, that uses a pressure that is measured for determining the weight being supported, and U.S. Pat. No. 4,533,274 to Moore shows a flexible joint that has annular elastomeric members arranged around a head that supports tension loads.